The present invention relates to a detecting method of a level of liquid in a cylindrical body, which can detect a level of liquid in a moving cylindrical body with high accuracy without direct contact of a ultrasonic transmitter and receiver with the surface of the cylindrical body.
When a liquid level or the like is detected by an ultrasonic probe, it is necessary to keep acoustically good contact between the surface of an object to be examined and an ultrasonic transmitter and/or receiver without an air layer or air bubbles. The reason is that detection of the ultrasonic is remarkably impeded due to a phenomenon such as absorption or scattering of a sound wave when the air layer or air bubbles are present in a propagation path of the sound wave.
The ultrasonic probe includes a vibration material for transmitting or receiving the ultrasonic and a contact means disposed in a propagation path to make the acoustic contact between the vibration material and the object to be examined.
As a conventional structure of the ultrasonic probe, there are known a type including contact means formed into various shapes and made of synthetic resin or metal in accordance with shapes and properties, and a type including a rubber balloon filled with liquid and disposed in front of a transmitting or receiving plane of ultrasonic to use it as the contact means.
However, the ultrasonic probe provided with the conventional contact means of synthetic resin or metal has a drawback that the object to be examined such as a moving object, an easily injured object or a flexible or soft object such as film is given wear, flaw, deformation, frictional heat or the like. Further, the ultrasonic probe equipped with the rubber balloon as the contact means has a problem that the flexible object such as film is pressed excessively and further the contact means can not come into contact with an object having a rugged surface sufficiently.
In a film manufacturing process, a pile agent is pushed out from an extruder to fill a parison in a cooling process with the pile agent, while it is necessary to detect a liquid surface of the filled pile agent. The detection and control of the liquid surface of the pile agent are required to stabilize a pressure within the parison, uniform a thickness of the parison and improve the quality of film manufactured from the parison. For example, when the conventional ultrasonic probe is used for the detection of the liquid surface, the parison in the cooling process is injured and deformed excessively. Accordingly, when the parison is expanded by the inflation method to manufacture a film product, the quality of the film product is degraded.
Further, a detecting apparatus of a liquid surface without contact involves a photoelectric liquid surface detecting apparatus. However, when this detecting apparatus is to detect the liquid surface in the parison, cooling water flowing along an outer periphery of the parison impedes transmission of light to thereby detect the liquid surface in error, and further when the parison is opaque, detection itself is impossible.
It is an object of the present invention to provide a liquid level detection method capable of detecting a level of liquid in a soft and moving cylindrical object to be examined such as an extruded parison in a cooling process with high accuracy.